2o8 LANG DON. [Vol. XI. 



to the cell near the circumference of the base. Some of these 

 cells simply taper into a mere fibre (PI. XIII, Fig. 15, /;■). The 

 larger number of such cells have a base which forks into two or 

 more basal processes (PI. XIII, Fig. i 5, c, d, n, vt). These pro- 

 cesses, which are usually varicose, descend in an irregular course 

 to the basement-membrane. In most cases they end at the 

 basement-membrane, but sometimes they extend along the 

 outer surface of this membrane for a short distance beneath 

 the neighboring cells. One of these processes, and only one, is 

 always produced into a nerve-fibre (PI. XIII, Fig. 5, 11, 12). In 

 cross sections it is often impossible to establish the connection 

 of some of the cells with nerve-fibres or to trace the course of 

 these fibres. In sections which pass obliquely through the 

 epidermis the connection of each cell with a nerve-fibre and 

 the course of these fibres along the base of the epidermis can 

 be clearly seen. 



Since but few of the sense-cells in a given section of an 

 organ are stained — frequently only one or two — it sometimes 

 appears as if these stained cells were not grouped into sense- 

 organs. But a study of such cases under the oil immersion 

 always reveals the fact that the cell in question is one of the 

 sense-cells of a sense-organ. In every case I have been able 

 to make out that the stained cell is but one of a group of cells 

 of similar shape, the rest remaining unstained, and that this 

 group is enclosed in covering cells which reveal the oval out- 

 line of the sense-organ. In almost every case a more or less 

 marltid elevation shows the summit of the sense-organ, and 

 this elevation usually bears a cluster of short sense-hairs. All 

 these facts clearly prove that every sense-cell in my preparations 

 which might be taken at first sight for an isolated cell is but 

 one of the sense-cells of a sense-organ. The sense-cells of some 

 of the sense-organs at the entrance to the buccal cavity were 

 found to be stained. These cells were like those of the epi- 

 dermal sense-organs, except that they were usually more slen- 

 der. The sense-organs of the buccal cavity itself were unstained 

 and the characteristic shape of their cells could not be made out ; 

 but the presence of the organ itself could usually be detected by 

 the convergence of the summits of the cells (PI. XIII, V'lg. 10). 



